1. Field of the Invention
The invention relates to a medical instrument comprising a tool at its distal end to be supplied with high frequency (HF) power, a HF power terminal and a HF power supply line extending from a proximal end region of the instrument to its distal end, wherein the HF power supply line is configured as a drive shaft for rotary drive of the tool and wherein contact means are provided which are electrically connected to the HF power terminal and electrically contact the drive shaft.
2. Description of the Related Art
Generally such medical instruments are normally used for removing soft tissue, where the instrument comprises a substantially fixed cutting tool. HF power can be supplied to the tool, i.e a high frequency (HF) voltage or a HF current. HF current, which flows when contacting the tissue, leads to strong heating in the region adjacent to the cutting tool (electrode so that tissue is removed and the cutting location is coagulated. Thus blood vessels are closed at the same time that tissue is removed and more serious bleeding is avoided.
WO96/2429 discloses a medical instrument, namely a morselator having a proximal end and a distal end carrying an electrode where distal end is insertable into a body cavity and containment vessel for morselating resected tissue. The electrical contact to a rotating tube is provided by brushes, wherein the tube carries a ring being in sliding contact with the brushes and an electric line connecting the ring with the electrode. A further medical instrument of the same kind is disclosed in DE 2545761 A1.
In view of the above, the object of the present invention is to provide an improved medical device of the mentioned type, where the contact between the power terminal and the drive shaft is improved.
According to the present invention, a medical instrument is provided of the mentioned type, the contact means comprising a spring means configured as a U-shaped element, whose two side-pieces carry a contact element and urge the contact element with a force acting in the direction of the drive shaft.
According to the present invention, a medical instrument is provided of the mentioned type, wherein the contact means comprise spring means which urge the contact element with a force acting in the direction of the drive shaft, the contact element is guided in a contact element guide, the spring means are arranged such that a force also acts in the direction of the guide surface of the contact element guide and the guide surface is congfigured as an electrical contact surface between the contact element guide and the contact element, so that an electrical connection results between the HF power terminal and the contact element via the contact guide element.
According to the present invention, a medical instrument is provided of the mentioned type, wherein the contact means comprise a housing which receives a section of the drive shaft and in which an electrically conductive fluid is contained in fluid-tight manner, so that an electrical connection between the drive shaft, the fluid and consequently the HF power terminal results.
The advantages of the aforementioned alternatives of the present invention are that the electrical contact between the power terminal and the drive shaft is improved due to the spring means urging the contact element reliably against the drive shaft so that a good electrical connection is guaranteed.
The latter alternative has the further advantage that the heat resulting from friction of the contact element with the drive shaft rotating at high speed is distinctly reduced. The size of the contact surface is maximized through the electrically conductive fluid, which completely encloses the drive shaft in circumferential direction. In addition, this alternative has the advantage that no air gap is present between the contact element and the drive shaft.
In a further preferred embodiment of the present invention, the electrical contacting of the drive shaft is provided over a contact surface.
The advantage is that the electrical field strength in the region of this interconnection is small despite the high HF voltage, where occurrence of spark discharges is avoided. In particular, the power transmission is optimized by the contact surface being as large as possible and by a small air gap. Furthermore, high frequency electromagnetic waves arise from spark discharges, which can lead to disturbances in other electrical devices. Precisely the highly sensitive medical devices could otherwise be disturbed by such spark discharges.
In a further preferred embodiment, the electrical contacting is performed over a surface corresponding to at least a part of the circumferential region of the drive shaft.
The advantage is that a very large connection surface is realized, so that the electric field is very small. The connection surface itself can be enlarged almost arbitrarily by extension in the longitudinal direction of the drive shaft. A further advantage is that the frictional forces per unit surface are reduced, so that the wear on the contact surface is reduced and heat arising from friction is minimized. In addition, the heat generated by power transmission is distinctly reduced.
In a further preferred embodiment, the contact means comprise a displacedable contact element, which is disposed in a contact element guide and which contacts the surface of the drive shaft via a contact surface, where preferably the contact surface of the contact element is adapted to the form of the drive shaft.
This has the advantage that a contacting of the drive shaft is achieved over a larger contact surface in simple constructive manner. Depending on the configuration, the contact surface can extend over one half of the circumference of the drive shaft. Furthermore, the heat generated through friction and power transmission can be well dissipated with the contact element guide.
In a further preferred embodiment, the spring means are arranged such that the force also acts in the direction of a guide surface of the contact element guide. Preferably, the guide surface is configured as an electrical contacting surface between the contact element guide and the contact element.
This arrangement of the spring means has the advantage that the contact element is reliably biased against the guide surface of the contact element guide, so that a good electrical and thermal connection is ensured between these two parts. The HF current thus can be supplied through the guide surface and the contact element lying adjacent thereto.
In a further preferred embodiment, the contact element contains a metal, preferably copper, and is produced as a contact block.
The advantage is that the contact element has a very good electrical conductivity, where however a high abrasion resistance is maintained.
In a further preferred embodiment, the guide surface of the contact element guide is gold-plated. Preferably the circumferential region of the drive shaft engaging with the contact means is coated with a good electrically conducting material, which is also corrosion resistant, preferably gold.
The advantage is that the electrical connection between the contact means and the drive shaft is further improved, so that the danger of spark discharge is also further reduced.
Further advantages and embodiments of the invention will become apparent from the description and the appended drawings. It will be understood that the above-mentioned features and those to be discussed below are applicable not only in the given combinations but may also be present in other combinations or taken alone without departing from the scope of the present invention.